refactor(config): Cleanup & permit selective override (#1940)

Permit certain config objects (i.e. MAX_BLOCK_LOOK_BACK) to be
selectively overridden, rather than requiring a complete definition. 
This will slightly improve new chain automation.

Also simplify a few instances of config parsing, adding some basic type
validation along the way.

src/common/Config.ts

@@ -35,7 +35,6 @@ export class CommonConfig {
       HUB_CHAIN_ID,
       POLLING_DELAY,
       MAX_BLOCK_LOOK_BACK,
-      MAX_TX_WAIT_DURATION,
       SEND_TRANSACTIONS,
       SPOKE_POOL_CHAINS_OVERRIDE,
       ACROSS_BOT_VERSION,
@@ -44,7 +43,20 @@ export class CommonConfig {
       ARWEAVE_GATEWAY,
     } = env;
 
+    const mergeConfig = <T>(config: T, envVar: string): T => {
+      const shallowCopy = { ...config };
+      Object.entries(JSON.parse(envVar ?? "{}")).forEach(([k, v]) => {
+        assert(
+          typeof v === typeof shallowCopy[k] || !isDefined(shallowCopy[k]),
+          `Invalid ${envVar} configuration on key ${k} (${typeof v} != ${typeof shallowCopy[k]})`
+        );
+        shallowCopy[k] = v;
+      });
+      return shallowCopy;
+    };
+
     this.version = ACROSS_BOT_VERSION ?? "unknown";
+    this.hubPoolChainId = Number(HUB_CHAIN_ID ?? CHAIN_IDs.MAINNET);
 
     this.timeToCache = Number(HUB_POOL_TIME_TO_CACHE ?? 60 * 60); // 1 hour by default.
     if (Number.isNaN(this.timeToCache) || this.timeToCache < 0) {
@@ -57,22 +69,18 @@ export class CommonConfig {
     this.maxConfigVersion = Number(ACROSS_MAX_CONFIG_VERSION ?? Constants.CONFIG_STORE_VERSION);
     assert(!isNaN(this.maxConfigVersion), `Invalid maximum config version: ${this.maxConfigVersion}`);
 
-    this.blockRangeEndBlockBuffer = BLOCK_RANGE_END_BLOCK_BUFFER
-      ? JSON.parse(BLOCK_RANGE_END_BLOCK_BUFFER)
-      : Constants.BUNDLE_END_BLOCK_BUFFERS;
+    this.blockRangeEndBlockBuffer = mergeConfig(Constants.BUNDLE_END_BLOCK_BUFFERS, BLOCK_RANGE_END_BLOCK_BUFFER);
 
     this.ignoredAddresses = JSON.parse(IGNORED_ADDRESSES ?? "[]").map((address) => ethers.utils.getAddress(address));
 
     // `maxRelayerLookBack` is how far we fetch events from, modifying the search config's 'fromBlock'
     this.maxRelayerLookBack = Number(MAX_RELAYER_DEPOSIT_LOOK_BACK ?? Constants.MAX_RELAYER_DEPOSIT_LOOK_BACK);
-    this.hubPoolChainId = Number(HUB_CHAIN_ID ?? CHAIN_IDs.MAINNET);
     this.pollingDelay = Number(POLLING_DELAY ?? 60);
-    this.spokePoolChainsOverride = SPOKE_POOL_CHAINS_OVERRIDE ? JSON.parse(SPOKE_POOL_CHAINS_OVERRIDE) : [];
-    this.maxBlockLookBack = MAX_BLOCK_LOOK_BACK ? JSON.parse(MAX_BLOCK_LOOK_BACK) : {};
-    if (Object.keys(this.maxBlockLookBack).length === 0) {
-      this.maxBlockLookBack = Constants.CHAIN_MAX_BLOCK_LOOKBACK;
-    }
-    this.maxTxWait = Number(MAX_TX_WAIT_DURATION ?? 180); // 3 minutes
+    this.spokePoolChainsOverride = JSON.parse(SPOKE_POOL_CHAINS_OVERRIDE ?? "[]");
+
+    // Inherit the default eth_getLogs block range config, then sub in any env-based overrides.
+    this.maxBlockLookBack = mergeConfig(Constants.CHAIN_MAX_BLOCK_LOOKBACK, MAX_BLOCK_LOOK_BACK);
+
     this.sendingTransactionsEnabled = SEND_TRANSACTIONS === "true";
 
     // Load the Arweave gateway from the environment.

src/relayer/RelayerConfig.ts

@@ -105,12 +105,8 @@ export class RelayerConfig extends CommonConfig {
     this.relayerDestinationChains = JSON.parse(RELAYER_DESTINATION_CHAINS ?? "[]");
 
     // Empty means all tokens.
-    this.relayerTokens = RELAYER_TOKENS
-      ? JSON.parse(RELAYER_TOKENS).map((token) => ethers.utils.getAddress(token))
-      : [];
-    this.slowDepositors = SLOW_DEPOSITORS
-      ? JSON.parse(SLOW_DEPOSITORS).map((depositor) => ethers.utils.getAddress(depositor))
-      : [];
+    this.relayerTokens = JSON.parse(RELAYER_TOKENS ?? "[]").map((token) => ethers.utils.getAddress(token));
+    this.slowDepositors = JSON.parse(SLOW_DEPOSITORS ?? "[]").map((depositor) => ethers.utils.getAddress(depositor));
 
     this.minRelayerFeePct = toBNWei(MIN_RELAYER_FEE_PCT || Constants.RELAYER_MIN_FEE_PCT);